1. Field of the Invention
The present general inventive concept relates to an inkjet printhead and a method of manufacturing the inkjet printhead, and more particularly, to a back-shooting type inkjet printhead that effectively dissipates heat generated from a heater to improve ink ejection characteristics, and a method of manufacturing the back-shooting type inkjet printhead.
2. Description of the Related Art
Generally, an inkjet printhead is a device for printing a color image on a printing medium by firing droplets of ink onto a desired region of the printing medium. There is a shuttle type inkjet printer and a line printing type inkjet printer. The shuttle type inkjet printer has an inkjet printhead that prints an image while the printhead moves in a direction perpendicular to the feeding direction of the printing medium. The line printing type inkjet printer is a recently developed high speed printer that has an array printhead having a width corresponding to the width of the printing medium. The array printhead includes a plurality of inkjet printheads that are arranged in a predetermined pattern. In the line printing type inkjet printer, the array printhead is fixed and the printing medium is fed past the array printhead for printing, so that high speed printing can be realized.
The inkjet printhead can be classified into two types according to the ejecting mechanism of the droplets of ink. The thermal type inkjet printhead creates bubbles with heat to eject the droplets of ink by the expansion of the bubbles, and the piezoelectric type inkjet printhead includes a piezoelectric material to eject the droplets of ink by utilizing pressure generated by the deformation of the piezoelectric material.
The ink droplet ejecting mechanism of the thermal printhead will now be more fully described. When a pulse current is applied to a heater formed of a resistive heating material, heat is generated from the heater to immediately increase the temperature of adjacent ink to about 300° C. As a result, bubbles are created, and the bubbles exert pressure on the ink filled in an ink chamber as the bubbles expand. The pressure pushes the ink out of the ink chamber through a nozzle in the form of droplets.
The thermal type inkjet printheads can be divided into three types depending on the growing direction of the bubbles and the ejecting direction of the droplets of ink. The three types of the thermal inkjet printheads are a top-shooting type inkjet printhead, a side-shooting type inkjet printhead, and a back-shooting type inkjet printhead. The growing direction of the bubbles and the ejecting direction of the droplets of ink are the same in the top-shooting type inkjet printhead, perpendicular to each other in the side-shooting type inkjet printhead, and opposite to each other in the back-shooting type inkjet printhead.
FIG. 1 is a side sectional view illustrating a conventional inkjet printhead disclosed in U.S. Pat. No. 5,841,452, as an example of a conventional back-shooting type inkjet printhead.
Referring to FIG. 1, an ink chamber 15 is formed in an upper portion of a substrate 10 to contain ink to be ejected, and an ink feedhole 17 is formed in a lower portion of the substrate 10 to supply ink to the ink chamber 15. Between the ink chamber 15 and the ink feedhole 17, a restrictor 13 is formed in a direction perpendicular to the surface of the substrate 10 to connect the ink chamber 15 and the ink feedhole 17. A nozzle plate 20 is stacked on the substrate 10, and the nozzle plate 20 is formed with a nozzle 21 to eject an ink droplet 30. The nozzle plate 20 includes a silicon oxide layer 23 formed on a surface of the substrate 10, heaters 22 formed on the silicon oxide layer 23 around the nozzle 21, and a passivation layer 25 protecting the heaters 22. In the passivation layer 25, thermal shunts 24 are provided to dissipate heat accumulated around the heater 22 toward the substrate 10 after the ink is ejected.
However, in the conventional inkjet printhead, heat remaining after the ink is ejected by the heater 22 is dissipated toward the substrate 10 through the silicon oxide layer 23, which has a low thermal conductivity. Therefore, a large amount of heat is accumulated in the nozzle plate 20 after the ink is ejected. The accumulated heat increases the temperature of the ink in the ink chamber 15, thereby changing the viscosity of the ink and deteriorating ejection characteristics of the ink.
Furthermore, the line printing type inkjet printers have been recently developed to satisfy the demand for high integration of the inkjet printhead and high speed printing. Such a line printing type inkjet printer generally employs the array printhead having the plurality of inkjet printheads. Since the array printhead is provided with a plurality of heaters, heat generated from the heaters and accumulated around the heaters is considerably large. Therefore, if the above-described conventional inkjet printheads are used for the array printhead, the ink-ejection characteristics of the array printhead are deteriorated much more.